recvFrom return value different from length of resulting string
Hey, I am trying to write a small haskell application which forwards udp messages. The complete program is here: http://hpaste.org/87681 Notice the lines: 43 (msg,bytes,addr) <- recvFrom sock 1024 44 putStrLn $ "Received: " ++ show bytes ++ " = " ++ (show . length $ msg) If I understand correctly, bytes is the number of bytes in the message. This should be äquivalent to (length msg), correct? Now I send an udp message (by connecting over the forwarded port with enet), and get this output: Received: 52 = 41 than I run it again, and get this output: Received: 52 = 43 Why is the length of msg not equal to 52? And why is it different from run to run? enet is unable to connect over this forward, by the way. Thanks! Nathan
It works when I am using Network.Socket.ByteString. I assume this is because the other recvFrom encodes the message with peekCStringLen, but I am not sure. Should the 2 implementations not behave the same besides returning a different datastructure for the received data?? On 05/10/2013 06:34 PM, Nathan Hüsken wrote:
Hey,
I am trying to write a small haskell application which forwards udp messages. The complete program is here: http://hpaste.org/87681
Notice the lines:
43 (msg,bytes,addr) <- recvFrom sock 1024 44 putStrLn $ "Received: " ++ show bytes ++ " = " ++ (show . length $ msg)
If I understand correctly, bytes is the number of bytes in the message. This should be äquivalent to (length msg), correct?
Now I send an udp message (by connecting over the forwarded port with enet), and get this output:
Received: 52 = 41
than I run it again, and get this output:
Received: 52 = 43
Why is the length of msg not equal to 52? And why is it different from run to run?
enet is unable to connect over this forward, by the way.
Thanks! Nathan
_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners
Unless your network data happens to be character data using the encoding
assumed by the functions in Network.Socket, bad things are going to happen.
Here is a quote from Network.Socket:
"Do not use the send and recv functions defined in this module in new code,
as they incorrectly represent binary data as a Unicode string. As a result,
these functions are inefficient and may lead to bugs in the program."
-Karl
On Fri, May 10, 2013 at 1:50 PM, Nathan Hüsken
It works when I am using Network.Socket.ByteString. I assume this is because the other recvFrom encodes the message with peekCStringLen, but I am not sure.
Should the 2 implementations not behave the same besides returning a different datastructure for the received data??
On 05/10/2013 06:34 PM, Nathan Hüsken wrote:
Hey,
I am trying to write a small haskell application which forwards udp messages. The complete program is here: http://hpaste.org/87681
Notice the lines:
43 (msg,bytes,addr) <- recvFrom sock 1024 44 putStrLn $ "Received: " ++ show bytes ++ " = " ++ (show . length $ msg)
If I understand correctly, bytes is the number of bytes in the message. This should be äquivalent to (length msg), correct?
Now I send an udp message (by connecting over the forwarded port with enet), and get this output:
Received: 52 = 41
than I run it again, and get this output:
Received: 52 = 43
Why is the length of msg not equal to 52? And why is it different from run to run?
enet is unable to connect over this forward, by the way.
Thanks! Nathan
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participants (2)
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Karl Voelker -
Nathan Hüsken